Thermal and Photophysical Properties of Highly Quadrupolar Liquid‐Crystalline Derivatives of the [ closo ‐B 12 H 12 ] 2− Anion

Two series of 1,12‐bis‐zwitterionic derivatives of the [ closo ‐B 12 H 12 ] 2− anion ( B ), containing either two 4‐alkoxypyridinium groups ( 1B[ n ]‐ p ) or one 4‐alkoxypyridinium and one 4‐pentylthianium groups ( 2B[ n ]‐ p ), were prepared and their structural (XRD, DFT), thermal, and photophysical properties were compared with those of the analogous derivatives of the [ closo ‐B 10 H 10 ] 2− anion ( 1A[ n ]‐ p and 2A[ n ]‐ p ). Some 1,7‐derivatives of B were isolated and investigated. Both series 1[ n ] and 2[ n ] exhibit nematic and crystalline polymorphism; the 12‐vertex derivatives ( B ) have higher transition temperatures than those of the 10‐vertex analogues ( A ). All compounds fluoresce with quantum yields higher for 1B ( Φ F =0.37 for 1B[7]‐ p and Φ F =0.27 for 2B[7]‐ p ) than those for the 10‐vertex analogues ( Φ F =0.04 for 2A[5]‐ p ). DFT calculations demonstrate an order of magnitude lower first hyperpolarizability, β (−ω,ω,0) , for 2B[7]‐ p than that for the 10‐vertex analogue 2A[7]‐ p (1.7×10 −30 vs. 18.9×10 −30  esu at ω =0).